New polyurethane pressure-sensitive adhesive products and processes

ABSTRACT

Very rapid catalytic formation and polymerization of polyurethane polymers followed by cross-linking with complex, hindered polyamines permits one-step, in-situ and continuous production of new types of pressure-sensitive adhesives and impregnated permeable materials. This pressure sensitive adhesive may be coated onto one side of a heat-resistant inert liner and then said adhesive coated side may be laminated to a matching sheet of cured rubber.

United States Patent [1 1 Dahl 1 NEW POLYURETHANE PRESSURE-SENSITIVE ADHESIVE PRODUCTS AND PROCESSES [75] Inventor: Rolf Dahl, West Columbia, SC.

[73] Assignee: Continental Tapes, Incorporated, Columbia, SC.

221 Filed: Mar. 22, 1972 [21] App]. No.: 236,959

Related US. Application Data [62] Division of Ser. No 50,953, June 29, 1970, Pat. No.

[52] US. Cl. 156/331, 117/122 P, 117/139,

117/161 KP, 156/230, 156/247, 260/22.26, 260/858 [51] Int. Cl. C09j 3/00, C09] 7/04 [58] Field of Search 156/230, 237, 247, 331;

[56] References Cited UNITED STATES PATENTS 3,330,713 7/1967 Watson et al 156/247 Primary Etuminer-Georg6 F. Lesmes Assistant Examiner-Paul J Thibodeau 5 7 ABSTRACT Very rapid catalytic formation and polymerization of polyurethane polymers followed by cross-linking with complex, hindered polyamines permits one-step, insitu and continuous production of new types of pressure-sensitive adhesives and impregnated permeable materials. This pressure sensitive adhesive may be v coated onto one side of a heat-resistant inert liner and then said adhesive coated side may be laminated to a matching sheet of cured rubber.

3 Claims, No Drawings NEW POLYURETHANE PRESSURE-SENSITIVE ADHESIVE PRODUCTS AND PROCESSES This application is a division of my copendingapplication, Ser. No. 50,953; filed June 29, 1970, now US. Pat. No. 3,761,307, issued Sept. 25, 1973.

As I have shown in my US. Pat. No. 3,437,622, certain polyurethane polymers can be used in place of the usual elastomers (natural and synthetic rubber) to produce pressure-sensitive adhesives. Furthermore, as shown in my copending application Ser. No. 23,983, series of 1960 and now US. Pat. No. 3,703,781, certain such polymers are of great advantage in impregnating certain permeable materials containing active hydrogen, such as paper, to greatly increase dry and wet strength and delamination resistance.

l have now discovered that such polymers suitable both for making pressure-sensitive adhesives and for such impregnation, can be formed and polymerized followed by cross-linking by reaction with certain polyamines, so rapidly in the presence of suitable catalysts as to permit the whole process to be carried out in one step and continuously. This, of course, results in marked simplification and cost reduction in forming a sheet or strip of adhesive which may be (1) formed separately and subsequently transferred to a backing material (2) applied directly to a backing material (3) impregnated into certain permeable materials or even (4) applied to certain permeable materials to impregnate them and, at the same time, leave thereon'a coating of pressure-sensitiveadhesive so as to yield, for example, a product that can be slit and wound to form'rolls of pressure-sensitive adhesive tape with an impregnated paper backing. My new procedures also,-of course, avoid the need for making a prepolymer as has been required heretofore.

The following Examples are illustrative of my procedures and products, modifications and extensions of which within the scope of my invention, will be apparem to those skilled in the art.

EXAMPLE 1.

92 grams of a trio] of hydroxyl number 48 and molecular weight about 3500 (Niax 1446, a polyether triol made by Union Carbide Chemicals Co., New York, N.Y.) was mixed with 8 grams of commercial tolylene diisocyanate (80 percent 2,4- and percent 2,6- tolylene diisocyanate, hereinafter sometimes called TDl), 0.8'gram 4,4-methylene-bis-o-chloroaniline, 1 gram stannous octoate catalyst, 40 grams of a 66% percent by weight solution in toluene of the glycerol ester of rosin and 40 grams of a 66% weight percent solution in toluene of non-heat-reactive phenolformaldehyde resin. The mix was immediately spread on an impregnated paper (see my copending application, Ser. No. 23,983, series of 1960 and now US Pat. No. 3,703,781) and dried and cured at 250F. for 2 to 3 minutes to yield a pressure-sensitive tape material containing 5 grams of cured and dry adhesive per square foot. The tape had good tack and remained well adhered to a polished steel surface on which it left no residue when stripped after being heated thereon for 17 minutes at 325F.

EXAMPLE 2.

92 grams of the triol of Example 1 was mixed with 7.4 grams TDI (OI-l: NCO equals 1:1), 40 grams of a 66% percent solution by weight of the glycerol ester of rosin in toluene, 40 grams of a 66% percent solution of nonheat-reactive phenol-formaldehyde resin in toluene and l gram'stannous octoate. The mix was immediately spread on an impregnated paper as in Example 1 and similarly dried and cured. The product was a good pressure-sensitive adhesive as in Example I but it left a slight residue after being adhered to a polished 'steel surface and heated for 17 minutes at 325F.

. EXAMPLE 3.

EXAMPLE 4.

As in Example 1, 92' grams of the same triol was heated at 212F. for about 1 hour until all the OH groups of the triol had reacted with 8 g. TDI mixed therein. To this prepolymer was added the same amounts of solutions of resins, diamine and catalyst as in Example 1 The mix had a useful life of about 2'hours before its viscosity became too high. The freshly-made mix was spread, dried and cross-linked as in Example I; but, of course, the procedure of Example 1 was much simpler and more economical. The product was similar to that of Example '1.

EXAMPLE 5.

The mix of Example 1, but without the solutions of rosin ester and phenol-formaldehyde resin, for which was substituted 26 grams of toluene as solvent, was coated on raw, untreated paper in amount to leave 5 g. dry'adhesive per sq.ft..on the coated side; The socoated paper was dried and cured as in Example 1. The paper backing was wet through by the solution and thoroughly impregnated but the solution did not run through-excessively to the back-side. The product was suitable as a protective tape (low adhesion) and the backing paper had increased, in dry tensile strength from 9 to 27 pounds perinch of width, the .wet tensile from 0 to 18 lbs/inch and the delamination resistance (force needed to continue splitting of the papers thickness) from 6 to 40 ounces per inch of width. If desired to' be provided in roll form, the backside can be treated with a release-coating material. Suitable such materials are applied in a solvent and comprise vinyl stearate, maleic anhydride, acrylic anhydride, polyamide or a silicone' EXAMPLE 6.

The adhesive solution of Example 1 was coated on the silicone-treated side of a high-density polyethylene strip or liner in amount to leave a final, 'dry coating of 10 grams per square foot. The adhesive-coated side of the liner was rolled up in contact with a matching strip of uncured natural rubber which had been compounded on a rubber mill to contain 50 wt. percent diatomaceous earth filler, 2.5 percent stearic acid, 1.7'percent sulfur and 0.4 percent of the vulcanizationaccelerator, mercaptobenzothiazole. A large roll was heated in an oven at 250F. for up to 24 hours in order to heat through the roll, evaporate the solvent and cure andcr'oss-li'nk theadhesive' and vulcanize the rubber backing. The product was agood pressure-sensitive adhesive that could be cut into sheets or slit and rolled into convolutely-wound rolls as desired. When used, the polyethylene liner released easily from'the adhesive and "the adhesive layer was firmly anchored to the cured rubber backing. The rubber used may be natural or syntheticfOther liners can be used as long as they will not adhere too strongly to the adhesive and will withstand the temperature. Suitable ones are strips or sheets of polypropylene or polyamide or polyester (Mylar). Normally they are provided with a release coating as mentioned above. After the required heating and curing, the cooled product must release the liner without substantially disrupting the adhesive layer or loosening-it fromits backing. Other inert, finelydivided fillers can be used such as pearlite, calcium carbonate'or clay; in amounts up to 50 percent by wt.

Other proportions of sulfur and vulcanization acceleratorscan be used such as listed in The Vanderbilt Latex Handbook, p.163, R. T. Vanderbilt Co., Inc., 230 Park Ave., New York, N.Y., 1954 edition.

' The ingredients of the adhesive can be continuously measured into a mixing chamber (with spiral vanes or mechanical stirrer) and continuously fed to coat upon a liner or backing which may pass directly and continuously through a drying and curing oven. When heated in roll form batchwise, of course, time must be allowed for theheat to penetrate to the interior of the roll-th larger the roll, the longer time.

Pigments such 'as titanium oxide may be used in amounts up to '10 wt. percent to color any of my adhesives which are normally transparent. Also antioxidants can be used in amounts of 0.5 to 1 wt. percent of the polyol, such as 2,6-di-tertiary-butyl-para cresol, butylated hydroxy toluene, phenyl-alpha-naphthylamine or v the condensation product of butyraldehyde and aniline;

' mere proximity, decrease the reactivity of the neighboring amino group and if the hindering group is bulky,

, the amino, group issterically hindered. Typical of suitable amines is 4,4'-methylene-bis-o-chloroaniline which is very effective and available. Other polyamines with suitably hindered amino groups are, for example, (1) alpha, alpha'-bi-p-toluidine (NI-I C H CH CH C H NH when it has a negative group such as Cl substituted on the benzene'ring next to each amino group (2) 3,3-dichlorobenzidine Nmclc mc n cmn which also has a, chlorine atom substituted'on the benzene ring next to (ortho to) each "amino group, (3) 3,3-dimethyl-benzidine (NH- CH C l-l C I-l Cl-l Nl-i which has a methyl group substituted on the benzene ring next to each amino group. In addition to having relatively inactive amino groups, my amines must thus have at least 2 amino Furthermore, it should be noted that such aryl amines,

as is the case with aniline, are readily halogenated (at least by chlorine or bromine) in an inert, non-aqueous solvent (such as acetic acid) to form substitution products with halogen ortho to the amino group, which makes amines such as l) and (2) above, readily available. lf adequate cross-linking does not occur in formation of my adhesives, they lack internal strength and heat-resistance. It is thus required that the amino groups be unreactive enough so that the polyols and isocyanates can react to form polyurethane polymers before the isocyanates extensively react with the amino groups and thus, presumably, that the amino groups react with isocyanate-gmup-terminated polymers and with residual isocyanate. It appears that the tin catalysts I use accelerate the formation of polyurethane polymers much more than they'accelerate reaction of isocyanate with amine groups. It should be noted that,

even thoughall OH groups in the polyols are reacted with'isocyanate, there still remain polymers with terminal isocyanate groups that can react with my amines. When lam operating a continuous process, my adhesive, as indicated, may also be-applied'to a backing material such as paper that has already been impregnated in anyof the usual ways, for example, with a synthetic rubber solution, or with my-polyurethane polymers usually without tackitying resin as in Example 5. Also the backing may be provided with a. release coating prior to my application of adhesive. Otherwise, a release coating may be applied between sections of the oven luse to dry and cure my-adhesive, using a roll coater under the web, which dips into a solution of the release coating; or the solution of release coating may be sprayed on the back-side of the web after r'ny-adhesive is partially driedand cured. Satisfactory release coatings are those herein described. To the usual materials I may also add 5 "10 wt. percent calcium stearate to impart a smooth, waxy feel.

I find it very satisfactory, as a method of mixing my adhesive solution ingredients, to meter themin liquid or solution form by means of diaphragm orproportioning pumps, for example, the TDI through one jet into a small chamber where it directly meets an opposing jet comprising a solution of the balance of the ingredients, namely for example, polyol, solvent, catalyst, resin and amine. The mix from the chamber is then directly coatedon the backing. Thus the mixing and coating are almost instaneous'; and the ingredients to be mixed are perfectly stable and can be prepared as much in advance of use as required. I

Catalysts I use are stannous octoate, dibutyl tin dilaurate, cobalt naphthenate, leadnaphthenate, bismuth naphthenate, lead laurate, phenyl mercuric benzoate, phenyl mercuric acetate, stannous neodecanoate, the stannous salts of the organic carboxyllic acids of l to 22 carbon atoms per molecule or any of these mixed with 10 to percent of their wt. of a tertiary amine from about 56 to 265 and of molecular weight from about 400 to 3,000; (2) triols of hydroxyl number from about 28 to 56 and molecular weight from about 3,000 to 10,000; (3) mixtures of the triols of (2) with to 90 percent by weight of the diols of l I prefer the above-described triols. These polyols include substituted or unsubstituted polyalkylene ether glycols, polyhydroxy polyalkylene ethers and especially the relatively cheap and readily available ethylene and propylene oxide adducts of diols and triols. Suitable polyols are also those of my copending application, Ser. No. 23,983, series of 1960 and now US. Pat. No. 3,703,781, comprising those of mol.wt. from about 800 to 3,500 and mixtures of polyols of mol.wt. from about 400 to 4,400 having average mol.wts. in the range from about 800 to 3,500. Similar polyhydroxy polyesters are also useable but are much more expensive and generally less satisfactory.

As tackifying resin I may use non-heat-reactive or heat-reactive phenol-formaldehyde resins, the latter having added polyol. These result in a firmer adhesive mass than with the other resins mentioned and the heat-reactive resin is used in adhesives for use above 250F. The use of these resins gives better aging and high temperature resistance and I prefer them.

Although I prefer any of the isomeric diisocyanates of toluene because of cheapness and availability, other aromatic polyisocyanates can be used such as those of ethyl benzene, xylene, bitolylene, biphenyl, diphenyl methane, methyl diphenyl methane, dianisidine, diphenylxenylene, dichloroxylene, dimethoxy biphenyl, etc. Herein, unless otherwise noted, by tolylene diisocyanate I mean any isomer or mixture of isomers of tolylene diisocyanate.

As solvents, although I prefer toluene, I may use benzene, xylene; toluene with up to 25 percent of its weight of heptane or other volatile, inert aliphatic or naphthenic hydrocarbons; acetatesof the monomethyl or monoethyl ether of ethylene glycol; ethyl or butyl acetate; or various volatile, inert ethers or ketones.

Tackifying resins are used in amounts from 0 to 100 percent of the weight of polyol. Such resins can be the ethylene glycol or glycerol esters of rosin or tall oil, terpene resins, coumarone-indene resins or polymerized unsaturated petroleum hydrocarbon residues. Gener ally I prefer resins and plasticizers of low acid number below about l0so as not to contain substantial capacity for reaction with isocyanate. Plasticizers to improve quick-stick, such as chlorinated diphenyl, the

ethylene glycol ester of rosin or the methyl ester of hy-' drogenated rosin, may be used in amounts from about 5 to 25 percent of the weight of polyol; but normally they are not needed. As a matter of fact I prefer in my simplified process to use as tackifying and plasticizing material only non-heat-reactive phenolformaldehyde resins in amounts from about 0 to 100 percent of the weight of polyol'since this gives better aging and heat resistance than the conventional materials. However, for adhesives to be used at temperatures above 250F., I may use a heat-reactive phenol-formaldehyde resin which is one containing polyol. Even without tackifying resin or plasticizer my adhesives are tacky enough for use as protective" tape.

It will be noted from my Examples that I use a small proportion of solvent when I am using a continuous process without formation of a prepolymer so that the adhesive can be spread directly without its running off or through the backing excessively. Thus my adhesive solution usually contains only 15 to 25 wt. percent solisocyanate-reactive hydrogenso called active hydrogen.

Having thus described my invention, what I claim is:

1. A simplified process for making a pressure sensitive adhesive product which comprises preparing a substantially uniform solution containing to weight percent solids in an inert,- volatile solvent of: l a polyol selected from the class consisting of (a) diols of hydroxyl number from about 56 to 265 and molecular weight from about 400 to 3,000 (b) triols of hydroxyl number from about 28 to 56 and molecular weight from about 3,000 to 10,000 and (c) mixtures of the diols of (a) in amount of 10 to percent by 7 weight, with the triols of (b); tackifying resin in amount from about 0 to percent of the weight of said polyols and selected from the class consisting of theethylene glycol and glycerol esters of rosin and tall oil,

coumarone-indene resins, terpene resins, polymerized unsaturated petroleum hydrocarbon residues, heatreactive and non-heat-reactive phenol-formaldehyde resins; (3) plasticizer in amount from about '5 to 25 per cent of the weight of said polyols and selected from the class consisting of chlorinated diphenyl and the methyl ester of hydrogenated rosin; (4) an aromatic polyamine in amount from about 80 to 100 percent of the equivalents of excess isocyanate to be used, wherein at least 2 of the amino groups are separated by a distance in the molecule at least about equal to that represented by the lengths of the groups selected from the class consisting of (a) 2 to 3 phenylene groups and (b) 2 phenylene groups plus 1 to 2 methylene groups, and wherein said amino groups are relatively unreactive, being hindered by negative groups in a position ortho to them, said negative groups being selected from at least one of the materials in the class consisting of chlorine, bromine, iodine, hydroxyl, ether, aromatic and aliphatic hydrocarbon radicals; (5) a catalyst in amount from about 0.5 to 5 percent of the weight of said polyol, that accelerates the polyol-isocyanate reaction; (6) an aromatic polyisocyanate in amount such that the ratio of isocyanate equivalents to equivalents of hydroxyl from said polyols is from about 1.1 to 2; coating the said adhesive solution on a heat-resistant inert liner sheet provided with a release coating on the side to be coated with the said adhesive solution, the adhesive-coated sideis laminated to a matching sheet of uncured rubber compounded with up to about 50 percent by weight of inert filler, sulfur and vulcanization accelerator and the soformed laminate is heated at a temperature of about 250F. for a time sufficient to substantially completely react the said polyisocyanate, evaporate the said solvent and cure the said rubber.

2. Theprocess of claim 1 wherein the said adhesive side of said liner is contacted with a backing material, the liner and contacting backing material is formed into a convolutely wound roll and heated batchwise in an tacted with said adhesive. 

2. The process of claim 1 wherein the said adhesive side of said liner is contacted with a backing material, the liner and contacting backing material is formed into a convolutely wound roll and heated batchwise in an oven to evaporate the solvent and substantially completely react the isocyanate groups, said liner being capable of being removed from said adhesive-coated backing material when removed from sAid oven and cooled, without substantially disrupting said adhesive or loosening it from its attachment to said backing material.
 3. The process of claim 2 wherein the said liner is selected from the class consisting of sheets of high-density polyethylene, polypropylene and polyamide, provided with a release coating on the side to be contacted with said adhesive. 